Effect of neuregulin-1 on histopathological and functional outcome after controlled cortical impact in mice

ErbB3 is a critical regulator of cytoskeletal dynamics in brain microvascular endothelial cells: Implications for vascular remodeling and blood brain barrier modulation

Neuregulin (NRG)1 - ErbB receptor signaling has been shown to play an important role in the biological function of peripheral microvascular endothelial cells. However, little is known about how NRG1/ErbB signaling impacts brain endothelial function and blood-brain barrier (BBB) properties. NRG1/ErbB pathways are affected by brain injury; when brain trauma was induced in mice in a controlled cortical impact model, endothelial ErbB3 gene expression was reduced to a greater extent than that of other NRG1 receptors. This finding suggests that ErbB3-mediated processes may be significantly compromised after injury, and that an understanding of ErbB3 function would be important in the of study of endothelial biology in the healthy and injured brain. Towards this goal, cultured brain microvascular endothelial cells were transfected with siRNA to ErbB3, resulting in alterations in F-actin organization and microtubule assembly, cell morphology, migration and angiogenic processes. Importantly, a significant increase in barrier permeability was observed when ErbB3 was downregulated, suggesting ErbB3 involvement in BBB regulation. Overall, these results indicate that neuregulin-1/ErbB3 signaling is intricately connected with the cytoskeletal processes of the brain endothelium and contributes to morphological and angiogenic changes as well as to BBB integrity.

Neuregulin-1/ErbB network: An emerging modulator of nervous system injury and repair

Neuregulin-1 (Nrg-1) is a member of the Neuregulin family of growth factors with essential roles in the developing and adult nervous system. Six different types of Nrg-1 (Nrg-1 type I-VI) and over 30 isoforms have been discovered; however, their specific roles are not fully determined. Nrg-1 signals through a complex network of protein-tyrosine kinase receptors, ErbB2, ErbB3, ErbB4 and multiple intracellular pathways. Genetic and pharmacological studies of Nrg-1 and ErbB receptors have identified a critical role for Nrg-1/ErbB network in neurodevelopment including neuronal migration, neural differentiation, myelination as well as formation of synapses and neuromuscular junctions. Nrg-1 signaling is best known for its characterized role in development and repair of the peripheral nervous system (PNS) due to its essential role in Schwann cell development, survival and myelination. However, our knowledge of the impact of Nrg-1/ErbB on the central nervous system (CNS) has emerged in recent years. Ongoing efforts have uncovered a multi-faceted role for Nrg-1 in regulating CNS injury and repair processes. In this review, we provide a timely overview of the most recent updates on Nrg-1 signaling and its role in nervous system injury and diseases. We will specifically highlight the emerging role of Nrg-1 in modulating the glial and immune responses and its capacity to foster neuroprotection and remyelination in CNS injury. Nrg-1/ErbB network is a key regulatory pathway in the developing nervous system; therefore, unraveling its role in neuropathology and repair can aid in development of new therapeutic approaches for nervous system injuries and associated disorders.

Ferroptosis Contributes to Neuronal Death and Functional Outcome After Traumatic Brain Injury

OBJECTIVES

Traumatic brain injury triggers multiple cell death pathways, possibly including ferroptosis-a recently described cell death pathway that results from accumulation of 15-lipoxygenase-mediated lipid oxidation products, specifically oxidized phosphatidylethanolamine containing arachidonic or adrenic acid. This study aimed to investigate whether ferroptosis contributed to the pathogenesis of in vitro and in vivo traumatic brain injury, and whether inhibition of 15-lipoxygenase provided neuroprotection.

DESIGN

Cell culture study and randomized controlled animal study.

SETTING

University research laboratory.

SUBJECTS

HT22 neuronal cell line and adult male C57BL/6 mice.

INTERVENTIONS

HT22 cells were subjected to pharmacologic induction of ferroptosis or mechanical stretch injury with and without administration of inhibitors of ferroptosis. Mice were subjected to sham or controlled cortical impact injury. Injured mice were randomized to receive vehicle or baicalein (12/15-lipoxygenase inhibitor) at 10-15 minutes postinjury.

MEASUREMENTS AND MAIN RESULTS

Pharmacologic inducers of ferroptosis and mechanical stretch injury resulted in cell death that was rescued by prototypical antiferroptotic agents including baicalein. Liquid chromatography tandem-mass spectrometry revealed the abundance of arachidonic/adrenic-phosphatidylethanolamine compared with other arachidonic/adrenic acid-containing phospholipids in the brain. Controlled cortical impact resulted in accumulation of oxidized phosphatidylethanolamine, increased expression of 15-lipoxygenase and acyl-CoA synthetase long-chain family member 4 (enzyme that generates substrate for the esterification of arachidonic/adrenic acid into phosphatidylethanolamine), and depletion of glutathione in the ipsilateral cortex. Postinjury administration of baicalein attenuated oxidation of arachidonic/adrenic acid-containing-phosphatidylethanolamine, decreased the number of terminal deoxynucleotidyl transferase dUTP nick-end labeling positive cells in the hippocampus, and improved spatial memory acquisition versus vehicle.

CONCLUSIONS

Biomarkers of ferroptotic death were increased after traumatic brain injury. Baicalein decreased ferroptotic phosphatidylethanolamine oxidation and improved outcome after controlled cortical impact, suggesting that 15-lipoxygenase pathway might be a valuable therapeutic target after traumatic brain injury.

Functional dissection of astrocyte-secreted proteins: Implications in brain health and diseases

Astrocytes, which are homeostatic cells of the central nervous system (CNS), display remarkable heterogeneity in their morphology and function. Besides their physical and metabolic support to neurons, astrocytes modulate the blood-brain barrier, regulate CNS synaptogenesis, guide axon pathfinding, maintain brain homeostasis, affect neuronal development and plasticity, and contribute to diverse neuropathologies via secreted proteins. The identification of astrocytic proteome and secretome profiles has provided new insights into the maintenance of neuronal health and survival, the pathogenesis of brain injury, and neurodegeneration. Recent advances in proteomics research have provided an excellent catalog of astrocyte-secreted proteins. This review categorizes astrocyte-secreted proteins and discusses evidence that astrocytes play a crucial role in neuronal activity and brain function. An in-depth understanding of astrocyte-secreted proteins and their pathways is pivotal for the development of novel strategies for restoring brain homeostasis, limiting brain injury/inflammation, counteracting neurodegeneration, and obtaining functional recovery.

Spatio-temporal assessment of the neuroprotective effects of neuregulin-1 on ischemic stroke lesions using MRI

The neuroprotective effects of neuregulin-1 (NRG-1) on stroke lesions were assessed longitudinally in rats with middle cerebral artery occlusion (MCAo) using MRI. Sprague-Dawley rats (n=16, 250±20g) underwent permanent MCAo surgery with cerebral blood flow (CBF) monitored by laser doppler flowmetry at ipsilateral side of bregma for 20min post-occlusion. A single 50μl bolus dose of NRG-1 or vehicle was administered into the left internal carotid artery immediately prior to MCAo. The expansion of the ischemic lesion into the cortex was attenuated by NRG-1 over a 48-hour (h) time span as measured by diffusion weighted imaging (DWI). The final infarct volumes of NRG-1 treated rats were significantly smaller than those of the vehicle treated rats at 48h (264.8±192.1 vs. 533.4±175.5mm(3), p<0.05). The NRG-1 treated rats were further subdivided into 2 subgroups according to their CBF reduction during stroke surgery: mild ischemia (<70% CBF reduction) or severe ischemia (>70% CBF reduction). In particular, ischemic infarction was not usually observed in the cortex of NRG-1 treated rats with mild ischemia at 3 and 48h post-occlusion. Histological results validated the imaging findings and demonstrated that NRG-1 treated rats had fewer injured neurons in peri-infarct areas 48h post-ischemia. In summary, the neuroprotective effect of NRG-1 in the pMCAo stroke model was demonstrated by prevention of ischemic lesion expansion, reduced infarct volume and protection of neurons from ischemic damage.

Neuregulin-1 inhibits neuroinflammatory responses in a rat model of organophosphate-nerve agent-induced delayed neuronal injury

Background

Neuregulin-1 (NRG-1) has been shown to act as a neuroprotectant in animal models of nerve agent intoxication and other acute brain injuries. We recently demonstrated that NRG-1 blocked delayed neuronal death in rats intoxicated with the organophosphate (OP) neurotoxin diisopropylflurophosphate (DFP). It has been proposed that inflammatory mediators are involved in the pathogenesis of OP neurotoxin-mediated brain damage.

Methods

We examined the influence of NRG-1 on inflammatory responses in the rat brain following DFP intoxication. Microglial activation was determined by immunohistchemistry using anti-CD11b and anti-ED1 antibodies. Gene expression profiling was performed with brain tissues using Affymetrix gene arrays and analyzed using the Ingenuity Pathway Analysis software. Cytokine mRNA levels following DFP and NRG-1 treatment was validated by real-time reverse transcription polymerase chain reaction (RT-PCR).

Results

DFP administration resulted in microglial activation in multiple brain regions, and this response was suppressed by treatment with NRG-1. Using microarray gene expression profiling, we observed that DFP increased mRNA levels of approximately 1,300 genes in the hippocampus 24 h after administration. NRG-1 treatment suppressed by 50% or more a small fraction of DFP-induced genes, which were primarily associated with inflammatory responses. Real-time RT-PCR confirmed that the mRNAs for pro-inflammatory cytokines interleukin-1β (IL-1β) and interleukin-6 (IL-6) were significantly increased following DFP exposure and that NRG-1 significantly attenuated this transcriptional response. In contrast, tumor necrosis factor α (TNFα) transcript levels were unchanged in both DFP and DFP + NRG-1 treated brains relative to controls.

Conclusion

Neuroprotection by NRG-1 against OP neurotoxicity is associated with the suppression of pro-inflammatory responses in brain microglia. These findings provide new insight regarding the molecular mechanisms involved in the neuroprotective role of NRG-1 in acute brain injuries.

Neuregulin1-β decreases IL-1β-induced neutrophil adhesion to human brain microvascular endothelial cells

Neuroinflammation contributes to the pathophysiology of diverse diseases including stroke, traumatic brain injury, Alzheimer's disease, Parkinson's disease, and multiple sclerosis, resulting in neurodegeneration and loss of neurological function. The response of the microvascular endothelium often contributes to neuroinflammation. One such response is the upregulation of endothelial adhesion molecules which facilitate neutrophil adhesion to the endothelium and their migration from blood to tissue. Neuregulin-1 (NRG1) is an endogenous growth factor which has been reported to have anti-inflammatory effects in experimental stroke models. We hypothesized that NRG1 would decrease the endothelial response to inflammation and result in a decrease in neutrophil adhesion to endothelial cells. We tested this hypothesis in an in vitro model of cytokine-induced endothelial injury, in which human brain microvascular endothelial cells (BMECs) were treated with IL-1β, along with co-incubation with vehicle or NRG1-β. Outcome measures included protein levels of endothelial ICAM-1, VCAM-1, and E-selectin, as well as the number of neutrophils that adhere to the endothelial monolayer. Our data show that NRG1-β decreased the levels of VCAM-1, E-selectin, and neutrophil adhesion to brain microvascular endothelial cells activated by IL1-β. These findings open new possibilities for investigating NRG1 in neuroprotective strategies in brain injury.

Neuregulin in cardiovascular development and disease

Studies in genetically modified mice have demonstrated that neuregulin-1 (NRG-1), along with the erythroblastic leukemia viral oncogene homolog (ErbB) 2, 3, and 4 receptor tyrosine kinases, is necessary for multiple aspects of cardiovascular development. These observations stimulated in vitro and in vivo animal studies, implicating NRG-1/ErbB signaling in the regulation of cardiac cell biology throughout life. Cardiovascular effects of ErbB2-targeted cancer therapies provide evidence in humans that ErbB signaling plays a role in the maintenance of cardiac function. These and other studies suggest a conceptual model in which a key function of NRG-1/ErbB signaling is to mediate adaptations of the heart to physiological and pathological stimuli through activation of intracellular kinase cascades that regulate tissue plasticity. Recent work implicates NRG-1/ErbB signaling in the regulation of multiple aspects of cardiovascular biology, including angiogenesis, blood pressure, and skeletal muscle responses to exercise. The therapeutic potential of recombinant NRG-1 as a potential treatment for heart failure has been demonstrated in animal models and is now being explored in clinical studies. NRG-1 is found in human serum and plasma, and it correlates with some clinical parameters, suggesting that it may have value as an indicator of prognosis. In this review, we bring together this growing literature on NRG-1 and its significance in cardiovascular development and disease.

Severe brief pressure-controlled hemorrhagic shock after traumatic brain injury exacerbates functional deficits and long-term neuropathological damage in mice

Hypotension after traumatic brain injury (TBI) worsens outcome. We published the first report of TBI plus hemorrhagic shock (HS) in mice using a volume-controlled approach and noted increased neuronal death. To rigorously control blood pressure during HS, a pressure-controlled HS model is required. Our hypothesis was that a brief, severe period of pressure-controlled HS after TBI in mice will exacerbate functional deficits and neuropathology versus TBI or HS alone. C57BL6 male mice were randomized into four groups (n=10/group): sham, HS, controlled cortical impact (CCI), and CCI+HS. We used a pressure-controlled shock phase (mean arterial pressure [MAP]=25-27 mm Hg for 35 min) and its treatment after mild to moderate CCI including, a 90 min pre-hospital phase, during which lactated Ringer's solution was given to maintain MAP >70 mm Hg, and a hospital phase, when the shed blood was re-infused. On days 14-20, the mice were evaluated in the Morris water maze (MWM, hidden platform paradigm). On day 21, the lesion and hemispheric volumes were quantified. Neuropathology and hippocampal neuron counts (hematoxylin and eosin [H&E], Fluoro-Jade B, and NeuN) were evaluated in the mice (n=60) at 24 h, 7 days, or 21 days (n=5/group/time point). HS reduced MAP during the shock phase in the HS and CCI+HS groups (p<0.05). Fluid requirements during the pre-hospital phase were greatest in the CCI+HS group (p<0.05), and were increased in HS versus sham and CCI animals (p<0.05). MWM latency was increased on days 14 and 15 after CCI+HS (p<0.05). Swim speed and visible platform latency were impaired in the CCI+HS group (p<0.05). CCI+HS animals had increased contusion volume versus the CCI group (p<0.05). Hemispheric volume loss was increased 33.3% in the CCI+HS versus CCI group (p<0.05). CA1 cell loss was seen in CCI+HS and CCI animals at 24 h and 7 days (p<0.05). CA3 cell loss was seen after CCI+HS (p<0.05 at 24 h and 7 days). CA1 cell loss at 21 days was seen only in CCI+HS animals (p<0.05). Brief, severe, pressure-controlled HS after CCI produces robust functional deficits and exacerbates neuropathology versus CCI or HS alone.

Neuregulin-1 effects on endothelial and blood-brain-barrier permeability after experimental injury

Blood-brain-barrier disruption occurs with a high incidence after traumatic brain injury, and is an important contributor to many pathological processes, including brain edema, inflammation, and neuronal cell death. Therefore, blood-brain-barrier integrity is an important potential therapeutic target in the treatment of the acute phase of brain trauma. In this short communication, we report our data showing that neuregulin-1 (NRG1), a growth factor with diverse functions in the CNS, ameliorates pathological increases in endothelial permeability and in BBB permeability in experimental models of injury. For in-vitro studies, rat brain endothelial cells were incubated with the inflammatory cytokine IL-1β, which caused an increase in permeability of the cell layer. Co-incubation with NRG1 ameliorated this permeability increase. For in-vivo studies, C57Bl mice were subjected to controlled cortical impact (CCI) under anesthesia, and BBB permeability was assessed by measuring the amount of Evans blue dye extravasation at 2h. NRG1 administered by tail-vein injection 10 minutes after CCI resulted in a decrease in Evans blue dye extravasation by 35%. Since Evans blue extravasation may result from an increase in BBB permeability or from bleeding due to trauma, hemoglobin ELISA was also performed at the same time point. There was a trend towards lower levels of hemoglobin extravasation in the NRG1 group, but the results did not reach statistical significance. MMP-9 activity was not different between groups at 2h. These data suggest that NRG1 has beneficial effects on endothelial permeability and BBB permeability following experimental trauma, and may have neuroprotective potential during CNS injury.

Neuregulin-1, the fetal endothelium, and brain damage in preterm newborns

OBJECTIVE

To assess the potential role for Neuregulin-1 (NRG1) as a systemic endogenous protector in the setting of perinatal inflammatory brain damage.

METHODS

We measured NRG1-protein and mRNA levels in human umbilical venous endothelial cells (HUVECs) of different gestational ages at various durations of exposure to lipopolysaccharide (LPS). In parallel, we genotyped the donor individuals for SNP8NRG221533, a disease-related single nucleotide polymorphism in the 5' region upstream of the NRG1 sequence. Intracellular NRG1 localization was visualized by confocal microscopy. Furthermore we analyzed the relationship between SNP8NRG221533 genotype and neurodevelopmental outcome in children born preterm.

RESULTS

We observed a positive dose-response-relationship between NRG1-mRNA and intracellular protein levels with both advancing gestational age and duration of LPS exposure in HUVECs. The presence of allele C at the SNP8NRG221533 locus was associated with an increased cellular production of NRG1 in HUVECs, and with a significantly reduced risk for cerebral palsy and developmental delay in children born preterm.

INTERPRETATION

In conclusion, our data indicate that gestational age, duration of LPS exposure, and the SNP8NRG221533 genotype affect NRG1 levels. Our results support the hypothesis that NRG1 may qualify as an endogenous protector during fetal development.

Neuregulin-1 high-producer genotype is associated with a decreased risk of admission to the neonatal intensive care unit

BACKGROUND

Neuregulin (NRG1) is a developmental growth factor and homozygous C allele carriers at the NRG221533 locus are at reduced risk for developmental disability.

AIMS

To explore whether 1) the NRG221533 CC genotype is associated with a decreased likelihood of neonatal intensive care unit (NICU) admission; 2) NRG1 is present in the infant's systemic circulation; and 3) to comparatively investigate two additional proposed high-producer single nucleotide polymorphisms (SNPs) for the cytokines interleukin 6 (-572) and interleukin 10 (-1082), examining both gene product and the association for admission to the NICU.

STUDY DESIGN

IL6 and IL10 protein was measured in umbilical cord blood by a multiplex sandwich immunoassay and NRG1 by ELISA. Infants were screened for SNPs IL6 (-572), IL10 (-1082), and NRG221533. We defined IL6 (C), IL10 (G) and NRG1 (C) as high-producer alleles based on published data.

SUBJECTS

Unselected single-center convenience sample of 97 newborns with a gestational age of 25-33 weeks (N=18), 34-36 weeks (N=17), 37-38 weeks (N=28), and 39-41 weeks (N=34).

OUTCOME MEASURES

Prematurity (<37 completed weeks) and admission to NICU.

RESULTS

The SNP NRG221533 CC genotype was associated with reduced admission to the NICU, even after adjustment for confounders. Adjustment for high IL6 levels reduced the protective effect. NRG1 levels tended to increase with advancing gestational age. Unexpectedly, we found lower IL6 and IL10 levels in infants homozygous for the IL6 (C) and IL10 (G) alleles, and no associations between IL10 (-1082) and IL6 (-572) genotype and prematurity or admission to NICU.

CONCLUSIONS

The NRG221533 CC genotype might be protective in newborns. The protective effect might not be directly related to increased systemic NRG levels.